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Wednesday, 28 January 2009

In Twilight World here at Bristol, can be seen a strange, newt like creature which visitors often walk straight past. This is a pity, because the axolotl is one of the strangest of amphibians, and is on the endangered species list.

Native to Lake Xochimilco, the axolotl (the name translates as “water dog” or “water monster”) is a member of a group of salamanders, the ambystomids or mole salamanders, which are native to North America. Several species are known, many with subspecies (which may be better treated as full species) and as a group the mole salamanders, like most salamanders, breed in water, laying eggs which hatch out into newt-like tadpoles. When they reach full size, which in some species can take 2 years, the tadpoles lose their external gills, start breathing air, and leave the water.

In the axolotl however, this does not take place. Instead the tadpole reached full sexual maturity and breeds while still in the larval state, a process called neoteny. This probable occurred because the climate around Lake Xochimilcho is quite severe, and it makes more sense for an amphibian to stay in the water all year.

Unfortunately, these days even the water is unsafe for the axolotl. Introduced Tilapia prey on them, and pollution and collection for food have also reduced their numbers. As a result, while they are well established in captivity, and have been since 1858 when they were first taken to Paris, in the wild they are endangered.

You might think that such a strange creature is unique, but in fact there are several similar forms of mole salamander known. The North American Tiger Salamander is known to produce occasional neotenous forms, especially in mountains or extreme environments, and these can still breed successfully with the metamorphosing form.

In addition, there are pure neotenous species known from Mexico. Anderson’s salamander comes from Laguna de Zacupa, and was collected in 1967 from a stream running into the lake. It appears to prefer moving water, rather than the still waters used by the Axolotl. Even more extreme is Taylor’s salamander from Laguna Alchichica, where it like deep water below 30m. Even stranger, Laguna Alchichica is quite brackish, with a salinity of 8.5g/l, making it quite a hostile environment for an amphibian.

One further point to note – it is not just amphibians which are neotenous. Many of the features which distinguish modern humans from other apes have been interpreted as neotenous – bare skin, a skull which looks at 90 degrees from the backbone instead of forwards along the axis of the spinal column, and a reduced extension of the facial bones. Adult humans look more like infants than for example adult gorillas look like babies, and human and gorilla infants are much more like each other than the adults of our two species are. So remember, a Mexican water monster may have more in common with you than you might think!

Sunday, 25 January 2009

Many of us will have watched TV wildlife series on South America and seen the brief glimpse that fortunate scientists manage to get of a Jaguar. These cats are extremely hard to see, confined as they are to dense rainforest, although a few Mexican Jaguars stray across the Rio Grande into southern Texas. However, they are the quintessential South American big cat.

So it is a bit surprising that the oldest known fossil Jaguars actually come from Europe – indeed some of the best preserved of them come from Westbury-sub-Mendip near Bristol at a cavern that filled in about 2 million years ago.

These fossil Jaguars, whose scientific name is Panthera gombaszoegensis, were slightly larger and more long-legged than the modern form, which suggests that they were more adept in open country than the forest adapted modern P.onca.

The range was not of course confined to Britain – in fact fossils have been found all over Europe and they probably also reached India. They must have reached into North East Asia because they crossed the Bering land bridge into North America about 1.5 million years ago.

About the same time, or slightly later, early Lions also crossed in to North America, and both species had a vast range – Jaguars of the modern form reached as far north as Nebraska during the Ice Ages and as far south as the tip of South America. Lions likewise reached South America, but it seems that the two species competed – fossil sites usually have one or the other but not both. Jaguars died out in the Old World during the Ice Ages but lions survived in North America until about 10,000 years ago.

The traffic across the Bering land bridge was not all one way – both Cheetahs and Pumas crossed from their ancestral home in North America into the Old World, and Pumas eventually reached Britain. However, Pumas died out in Eurasia and Cheetahs died out in North America at the end of the last Ice Age, at the same time as most other large mammals in North America – including Pumas (modern North American pumas descend from South American survivors).

What does this mean for conservation? Well, first of all, we need to be careful when we talk about an animals “natural” range. An animals’ range may be its current range (where it lives now), its historic range (where it lived when people started taking notes about it), or its prehistoric range (where it used to live) – and this last may not even be on the same continent as the current range.

We should also consider its future range – as the environment changes for reasons both human and natural the place where an animal lives now may progressively cease to be suitable, while other parts of the world may become ideal if it could expand its range to the area. Because of barriers to migration, whether these are oceans, rivers, or just farmland or other man-made habitats a creature cannot cross, nature reserves run the risk of becoming (as one article I read put it) “condemned cells” where species slowly fade away. The only solution is to seriously consider introductions of species outside their current range, although this too is obviously a potential risk to existing faunas. Mostly this applies to mammals – most birds will simply fly to suitable habitat as soon as it becomes available ( for example, Little Egrets have colonised the UK in recent years as a result of a warming climate). However in the case of large predators human resistance will be understandably intense – would people in this country support reintroduction of Brown Bear or Wolf? – or people in Bulgaria support reintroduction of lions – which survived in the Balkans until at least 400 BC? This is not as out of the box as its sounds – some activists have seriously suggested the introduction of the modern relatives of extinct North American large mammals such as Elephants, Cheetahs, even Lions, as a way of “repairing” the lost ecosystem of pre-human North America.

Friday, 23 January 2009

I went up to Slimbridge this morning on a birding trip. For those readers who do not know it, Slimbridge is a bird reserve north of Bristol on the Severn estuary that was founded by Sir Peter Scott, the naturalist, painter, and son of Scott of the Antarctic.

The reserve is basically in two parts, a central area with a wildfowl collection, and a surrounding area managed to attract wetland birds, especially wintering wildfowl for which the area has long been famous.

Slimbridge has widened it’s focus from wildfowl to other wetland birds in its collection. It is working on the initial stages of a re-introduction plan for Eurasian Crane to the south west of England. These magnificent birds died out at least 500 years ago as a result of hunting and drainage of suitable habitat, but some years ago they naturally recolonised Norfolk in the east of England. The greatest birding experience of my life was when, on a birding holiday there, I was present when the first chick fledged. We had stopped to watch some golden plovers in a field on a very foggy day, when we heard a trumpeting sound through the mist. Our guide at once said “those are cranes!” and of course we all said “what?!” as we did not even know they were in the area. The pair came down and landed only a few hundred metres from us, accompanies by their chick, and at once went into their triumphant dance display.

Since then, the Norfolk population has slowly grown, but in any one year the available habitat can only support perhaps 5 pairs at the most, so it was decided to try to establish them elsewhere. Slimbridge is hand raising crane chicks from either wild nests or captive bred adults, and these birds will eventually be released into a fenced off area of suitable marshland. Although the adult birds are pinioned, the young will be left to fly free and hopefully establish themselves in the area.

Slimbridge is also currently developing a wetland mammal exhibit. This is due to open May this year, and will show a wetland as it was before human interference became significant. Among the animals on show will be Beaver, Otter, Water Shrew, Harvest Mouse as well as Common Cranes and other birds that will probably fly in on their own. There is also planned to be some larger land animals that you might find in such areas, possibly including Heck Cattle, which is a breed created in the twenties to resemble the extinct Aurochs. I will let you know once it opens and describe it then.

Well, back to today’s trip. It was only a few hours but the bird list includes these:

Monday, 19 January 2009

Prowling through the forests of West Africa and Asia are a group of nocturnal primates distantly related to bushbabies and lemurs. Varying in size from a half grown guinea pig to a ring-tailed lemur, the lorises are an ancient group, with a fossil record dating back 40 million years or more.

A member of the loris family is easily recognised. The tail is short or absent, the hands are modified to give a good grip on slender vines and branches, and the very large eyes face forwards. They do not jump, but instead move methodically through the forest with something of the gait of a chameleon. In many ways, they behave almost like chameleons, and their hands are modified by the reduction of the second digit which gives their hands a very chameleon-like appearance. As with chameleons, they seldom drink standing water, but have been seen to lick raindrops off leaves.

The number of species of loris is at present uncertain. As with many nocturnal animals, they rely on scent or call to distinguish each other, and as a result different species are hard to tell apart. At present the total is as follows:

1) Loris. The slender lorises, with two species and at least 6 identifiable forms. Found from India and Sri Lanka2) Nycticebus. The slow lorises, with two species and numerous regional varieties. Found in South East Asia3) Arctocebus. The Angwantibos. 2 species in West Africa4) Perodictus. The Potto. At least 3 forms, also in West Africa

Unfortunately many today, especially in Asia, are highly threatened. The main reason, as you might expect, is deforestation. Lorises are specialised for clambering through dense tangles of vines and other undergrowth, mostly within 5 metres of the ground, and are not famed for their speed, although they can move fast when they want. As a result, they are easy to catch, and their undeniably cute appearance means they are captured for a local pet trade. They are also used in local medicines.

Lorises have historically not done well as captive animals, and for most species there is no viable captive population, and why this is so has only recently been understood.

Most importantly, the diet of lorises is unusual for a primate. As is well known, practically all primates are mainly vegetarian. Some prefer leaves, others fruit, some add gum or sap, but animal food is a small part of the diet. Smaller primates often eat a lot of insects, and larger ones like chimpanzees or baboons will even catch monkeys or gazelle fawns, but generally faced with an unfamiliar species a selection of fruit and leaves plus some insects will at least give a start on working out the ideal captive diet.

Lorises however are quite different proposition. The vast proportion of their diet is composed of insects and animal prey, to which they are attracted by movement. Slender lorises, which in some species are lemur sized, frequently catch birds almost their own size (although stories of them catching peacocks are probably mythical). Slow lorises eat slightly more plant material, especially gum and sap, but they too catch many insects. Much of the typical insect prey of a loris is toxic or unpalatable, such as poisonous ants or hairy caterpillars, but they prefer tastier prey like lizards where possible. Although slow moving when travelling, lorises have a very fast grab, and when catching birds will usually bite the head of the prey to kill it.

As a result of these dietary specialisations, lorises are prone when fed on a diet high in sugars from fruits and lacking in insect and animal protein to develop kidney disease, diabetes, and dental disease, with predictable results.

The other main problem with captive lorises is that despite their size they pose a serious risk to people coming in contact with them. A slow moving, easily captured species needs some defence, and lorises have a defense unique among primates, and very rare among mammals – they have a poisonous bite. The loris “arms” itself by licking glands on its arms, and an enzyme in the saliva then transforms the secretion into one capable of causing serious allergic reactions, even death, after biting its attackers. The same poisonous saliva is used by the mother to protect her infants – before “parking” them on a branch before going off to feed she licks them all over, rendering them distasteful to predators at the least. The loris has a stereotyped threat display where they hold their arms over their head, with the brachial glands at the ready, and I personally suspect that the contrasting head patterns many lorises show may actually constitute warning colouration to reinforce the display.

Although as I mentioned earlier lorises are seldom kept in captivity, we are fortunate to have the pygmy slow loris here at Bristol in Twilight World, and have bred them on several occasions. Ranging into southern China, the pygmy slow loris reaches quite high elevations, and in the winter months puts on a considerable amount of weight and goes into a near torpor.

Well, what are the implications of all this for the loris? First of all, it shows the importance of field studies. Animals in captivity can be the source of valuable information, but studies of wild animals are vital to enable us to provide what animals actually need in captivity, instead of what we think they need. The other is what amazing animals they are, and how vital it is that they are conserved in the wild for future generations.

Sunday, 18 January 2009

For the very large group of people for whom this heading means nothing, last Saturday I went to the annual general meeting of the Phasmid Study Group at the Natural History Museum in London. For those who do not know what a phasmid is – phasmids are the scientific name for the group known as stick insects (walking sticks in the US).

I joined the PSG a few years ago when they did a display here at the zoo. I have always been interested in animals of all kinds, and until you see the range of species it is hard to appreciate the range of camouflage options these creatures use.

Membership of the PSG is open to all – annual membership is 12 pounds and gives a quarterly newsletter and access to a very extensive database of information, as well as a livestock list – eggs of many species can be sent through the post.

Stick insects are most closely related to the grasshoppers and crickets, and probably first appeared in the Cretaceous, as most of them feed on flowering plants and these did not appear until that point. They have a fairly straightforward life history, the newly hatched nymphs progressing smoothly towards the adult form with no major changes in the way that butterflies and moths do for example. However, many species are either sometimes or permanently parthenogenetic, with adult females laying fertile eggs without mating. In species with males, the males are often winged and the females wingless.

We have several species of phasmid here at Bristol. In Bugworld we have the Giant stick insect (Pharnacia), The Malay Jungle Nymph ((Heteropteryx), Leaf Insects (Phyllium) and Macleay’s Spectre (Extatosoma). The volunteers also have a colony of the Giant Spiny Stick (Eurycantha) that we use in Animal Encounters.

To get back to the AGM, the meeting had the usual reports from various secretaries, and two slide shows, one from a collecting expedition to the Philippines from which they brought back several species to study and culture, and a report from one of the academic members of the PSG from the International Congress of Entomology held last year in Dubai.

The last part of the meeting was a livestock distribution. As anyone who has kept phasmids knows, many species are quite prolific, and the January and July meetings are an opportunity to bring in surplus stock and exchange them for new and interesting species. I brought home several new species this time, which I will endeavour to breed. One of those I have bred is the “Black Beauty” Peruphasma schultei (picture at head of post). Although only from a restricted area in Peru, it is extremely prolific and easy to keep in captivity, and its beautiful colours (which are designed to warn off potential predators of a toxic spray it can produce) have made it one of the more popular recent discoveries.

Having travelled to Cyprus on a birdwatching holiday, I thought people might be interested in some of my observations of the natural history, and especially the birdlife, of the island. The Greek islands are of course well known to holidaymakers, but perhaps less known is that prior to the arrival of human hunters and farmers about 9,000 years ago many, especially the larger islands, were home to animals as strange as you might find on Madagascar or South East Asia today. All the larger animals are now extinct, but some of the birds and reptiles, and many of the plants and insects, can still be found if you know what and where to look.

Geologically, Cyprus is a piece of deep sea floor which has been thrust up above sea level by the collision of the African and European tectonic plates. It is separated by a considerable distance from the mainland, at least today, and as a result colonisation by terrestrial plants and animals is difficult. Changes in sea level and what was at some time presumably a brief land collection have allowed colonisation by oaks and some other plants which are unlikely to disperse far by sea.

The isolation has resulted in a large percentage, nearly 10%, of the flora being endemic, often with connections to what are now widely dispersed floral elements. One species of berry-bearing bush for example has its closest relatives in the Canary Islands and Nepal.

I did not have much time to study the insects, but there is one species of endemic butterfly, the Paphos Blue, which is widely seen around the island. Other butterflies have as might be expected connections in the Middle East or Greece, although there are some also found in North Africa.

Most of the endemic mammals once found on the island are unfortunately extinct. The most spectacular was a pigmy hippopotamus, about the size of ours but not closely related, which seems to have been more adapted to a terrestrial life. Standing water is very scarce on Cyprus, and the oak forest which once covered most of the island would have provided ample cover.

There are only two endemic mammals remaining, the fairly widespread Cyprus Long-Eared Hedgehog and the only recently discovered Cyprus Mouse. The Cyprus Spiny Mouse, similar to the Turkish Spiny Mouse we have here at Bristol, has not been seen since 1980 and is believed to be extinct. The other mammals on the island, including the local form of the Mouflon, are almost certainly the result of early human introductions.

There are a range of reptiles and 3 amphibians on the island. As amphibians cannot cross the sea easily, they may have also been human introductions, whether accidental or deliberate. One of the reptiles is endemic, the Cyprus Whipsnake, and several others have distinct local subspecies.

However, my main focus was on the birds. I managed to see such endemic species as the Cyprus Warbler, Cyprus Wheatear, and Cyprus Scops Owl, and also several local subspecies of more widely spread birds, at least one of which, The Cyprus Coal Tit, is very distinctive in call and appearance and is probably best considered a separate species. The total bird list for my group came to 140 species, and Cyprus as a whole has a list of over 300, most being migrants passing through from Africa.

The Cyprus Wheatear is particularly interesting, as it shows a divergence in habitat from its close relatives. Wheatears are a group of mainly Mediterranean small songbirds similar to Stonechats, and are almost always found in open country. Only a single species reaches the UK, where it breeds in grassland and moors. The Cyprus Wheatear on the other hand is if anything commoner in woods than in the open fields, and behaves more like a Redstart or flycatcher.

Wildlife in Cyprus is fairly easy to find, but the conservation status of the island needs a lot of work. Especially along the coasts, holiday development threatens to destroy a lot of the remaining space for wildlife, and pollution and introduced species of animals and plants threaten to overrun many areas. Unfortunately, hunting is also widespread and many migrant birds are killed each year.

To sum up, if you are thinking of travelling to Cyprus on holiday, don’t forget your binoculars and please help any environmental bodies you meet – they need all the help they can get

Monday, 12 January 2009

As everyone knows, about 65 million years ago there was a catastrophic mass extinction, which resulted in the extinction of the dinosaurs and the rise of the mammals. There is only one problem, it is not actually true. In fact, there are dinosaurs all over the world today, including your back gardens, and one of the largest surviving species are at Bristol Zoo, the cassowaries.

Ok, let me explain. It has been known for some years that birds evolved from dinosaurs, but recent discoveries from China have produced beautifully preserved fossil specimens showing feather and soft part impressions, and has enabled a much clearer picture to be formed of the origin of birds and their relationship with their closest relatives.

One of the most significant discoveries is that feathers, at least of the hair-like forms found on cassowaries and emus, actually developed at an early stage, and were universal in the later bipedal carnivorous dinosaurs. Large species are known from fossil skin impressions to have had leathery or scaly skin, but this is simply because large animals do not need to retain body heat and do not need insulation. Small species, and possibly juveniles of large species, probably looked very bird-like in life. For example, the early tyrannosaur Di long (about the size of one of our Dwarf Crocodiles), had distinct feather impressions on the tail of the fossil that was found, and after examination of the arm bones it became clear that Velociraptor had feathers on its arms as the bones had the attachment points for large feathers.

The care of the young was also very bird-like in these small dinosaurs. A fossil has been found of a raptor still on its nest incubating its eggs (it was caught in a sandstorm), and at least some post-hatching nest care is very likely.

So if these dinosaurs looked liked birds, what more can we discover from their descendants?

Scattered over most of the southern hemisphere are a group of mostly large, flightless birds (and some recently extinct species) which together belong to the group known as the ratites. This group, including the Ostrich, the two South American Rheas, the several species of Kiwi, the Emu and the three species of cassowaries, together make up the oldest branch on the family tree of modern birds, and probably split off from the lineage leading to more advanced species well before the end of the age of dinosaurs. In size they are in fact towards the top end of the more bird-like therapods (the Velociraptor in real life stood about 1 metre tall and probably ate animals no bigger than rabbits or chickens)

In fact, you could look at our cassowary and the only distinctive feature that sets it apart from later therapods is the loss of the tail, which like all birds is reduced to a set of fused bones supporting the tail feathers. Otherwise, you could put them in a line up with Cretaceous dinosaurs and not notice a major difference.

The question has been asked in the past as to how the ratite species became so widespread, and there are two scenarios proposed. One is that the common ancestor of all ratites was flightless and the various species evolved as the continents drifted apart. The other is that the common ancestor could fly became flightless later.

It is at this point that a group of pheasant or quail-like birds of South America enter the picture. The tinamous have several features in common with the ratites, and have long been recognised as a side branch of the same stock. Recent genetic work however has identified them as belonging to the same branch that gave rise to the cassowaries, emu and kiwis, and this implies that these birds at least dispersed by flying and became flightless later. It might seem surprising that the nearest relatives of the cassowary live in the Andes, but before continental drift split the continents and climate change made Antarctica freeze over all the southern continents were joined in a temperate and well vegetated southern supercontinent called Gondwana. Many animals ranged over the whole supercontinent, which is why today both South America and Australia have marsupials.

One other interesting fact about the ratites – most of them (including the tinamous) have a nesting system where the male does a great deal, or in some species all, of the incubation and chick care. This must date back to the origins of the group, which means that if we found a fossil ratite from over 100 million years ago we could make a good guess as to how it looked after its young.

In just about every description in popular literature crocodiles tend to be described as “ancient”, “primitive” or “unchanged”. Actually, this is far from the case, and the fossil history of crocodiles is as full of strange forms and unlikely lifestyles as any other group of animals.

The fossil record of crocodiles is indeed very long, the first known forms date back to the early Triassic. However, these were very different in appearance to modern forms, being small (about 1m), terrestrial, and in some species at least probably bipedal. They can be recognised as crocodiles however by details of the ankle joint and pelvis which are unique to the crocodiles and distinguish them from early dinosaurs.

During the age of dinosaurs most crocodiles became increasingly adapted to an aquatic lifestyle, producing among others the Metriorhynchids, fully marine forms with paddles for limbs and tail flukes, which however probably still laid eggs on land.

The modern crocodiles are divided into three groups, the Alligatoridae (Alligators and Caimans, 8 species), the Gavialidae (Gharials, 1 species) and the Crocodylidae (13 species). The number of species is likely to grow – the Spectacled Caiman for example is quite variable over its range and probably represents several separate species.

All the modern groups can trace their ancestry back to the Cretaceous period, the last part of the age of dinosaurs. Although crocodiles include the largest living reptiles, the Saltwater Crocodile of Australasia can grow to over 6m for example, they are dwarfed by fossil forms. The late Cretaceous Deinsosuchus (an alligator) grew to perhaps 15m for example, and even more recent forms could be similar in size – the giant Brazilian caiman Purrasaurus from perhaps 15 million years ago reached 12m (the size of a Tyrannosaurus rex!).

In the Cretaceous some crocodiles became terrestrial predators. The Sebecosuchids had a more upright gait and dinosaur-like teeth, and must have been significant predators in terrestrial ecosystems. Interestingly, these survived the end-Cretaceous mass extinction by at least 15 million years. Other forms became herbivorous, at least judging by their teeth.

Our own crocodiles here at Bristol are of course Dwarf Crocodiles, Osteolaemus. Thought until recently to be a single species, they have recently been split into three. Fortunately our own animals have been identified as belonging to the same species, the nominate form O.tetraspis. Crocodiles hybridize freely in captivity, which poses considerable problems for conservation breeding.

Although modern crocodiles are thought of as pure carnivores, some at least take some vegetable matter. It was thought until recently that any vegetation found in a crocodiles stomach was eaten by accident, but I have seen film of a (captive) alligator in Florida deliberately picking kumquats out of a bush in its enclosure, and it is possible that some wild caiman do much the same, at least in the rainy season when fish are harder to catch.

A few words of introduction. For nearly 15 years now I have been a volunteer at Bristol Zoo, where I do talks to the public and occaisionally also do what we call outreach events where we take some animals out to the public. My intention is to blog about being a volunteer and also write some articles about the animals I have seen at Bristol and other zoos, and maybe also about the birdwatching trips I have been on.